Structural reinforcement can be provided by the provision of a reinforcing member within a hollow structure such as part of an automotive frame. It is known that the reinforcing member may comprise a core, typically a hollow core of metal or rigid plastic, carrying a structural adhesive foam. In the known processes the foam is expanded when heated to bridge the small gap between the core and the hollow structure so that the core is bonded to the hollow structure. Typically the nature of the structural adhesive foam is chosen so that it expands at the temperatures used to bake the coating that is applied to the hollow structure during the e-coat anti-corrosion coating technique widely used in the automobile industry.
It has not however been possible to apply these techniques to provide satisfactory reinforcement to those areas of an automobile where the reinforcement is to be provided behind the internal surface adjacent to external panels of the vehicle. This problem, sometimes known as read through, has arisen because the foam tends to shrink as it cools after foaming which can cause unsightly deformation of the external panels of the vehicle which tend to be made of thin flexible sheet metal.
The invention therefore provides a system whereby reinforcement can be provided to external panels of automobiles without causing deformation of the external surface of the external panel.
European Patent 1256512 addresses this problem and provides a cap to cover the foam in the areas that it contacts the outer panels. This cap is however expensive and can make the production and assembly of the part complicated.
The trends in motor vehicle design are towards lighter vehicles to improve fuel consumption. At the same time the safety standards and requirements are becoming more rigorous as indicated by the European Union requirements and the Euro-NCAP impact testing. The use of lighter materials such as aluminum to produce the hollow cross-sectional members that are used as vehicle sub frames has lead to the need for additional reinforcement. There is also a need for reinforcement behind external panels in various locations in the vehicle such as in window and door surrounds particularly in cavities between window and door frames and external panels such as in the reinforcement of hatchback doors and windscreen pillars where they connect with the roof of the vehicle.
There are four main types of application where structural reinforcement is required in vehicles. Crash protection where the prevention of vehicle body deformation is important to provide protection for the occupants. Energy absorption to enhance performance after yield. The reduction of flexing or body movement in the vehicle structure particularly to improve durability and reduce stress cracking and the point mobility problems requiring the reduction of resonance by the provision of stiffening. The need for reinforcement is present irrespective of the materials that are used to produce the vehicle structure and the need varies from material to material according to the nature of the reinforcement that is being provided. The reinforcing parts can also reduce the noise created by the motion of a vehicle by having a sound deadening effect as a result of blocking air paths in cavities.
It is known to provide longitudinal reinforcing structures within the hollow cross sections of vehicles. For example, PCT Publication WO97/43501 provides a beam, which can be mounted within the cross section to provide reinforcement along one axis in a hollow structure. The beam is provided with an expandable adhesive on two surfaces, which can be foamed upon heating to bond the beam to two opposed walls of the cross section. This technique is not suitable for use in the electrocoat process. Furthermore, the beam will only provide significant reinforcement along the axis of the beam. In WO97/43501 the beam with foamable material on opposed surfaces is placed in the cavity and subsequently foamed under the action of heat. This will result in uneven foaming and to non-uniform foam structures since on the underside the foam must raise the weight of the beam whereas expansion on the topside is free.
It is also known to provide foamable plastic molding within the hollow cross sections, these moldings can be foamed upon application of heat, such as is provided by the baking step in the electrocoat process, to provide a foamed baffle that fills the cross-section to provide sound adsorption. Such systems are described in European patent applications 0383498 and 0611778. The foam baffle provides sound deadening and vibration resistance. In these systems the entire insert is foamable and it is proposed that the foamable material be chosen so that it will foam during the baking process, which follows the electrocoat process typically used in vehicle manufacture to provide resistance to metal corrosion. The materials of these patents are not however reinforcing materials but are used to provide acoustic baffles and seals.
In the electrocoat process a vehicle structure is immersed in a bath of coating fluid from which an anticorrosion coating is deposited on the metal by electrolysis. The vehicle metal structure is subsequently heated to bake the coating on the metal. The electrocoat process is typically applied to complete vehicle structures in which hollow sections have been capped. Accordingly reinforcing structures are preferably provided within hollow sections prior to the electrocoat. It is therefore important that the reinforcing structure have minimal impact on the operation and efficiency of the electrocoat process.
A problem associated with both the reinforcing materials and the baffles is that if they are provided to produce foam adjacent to an external metal panel the shrinkage of the foam as it cools after expansion can cause undesirable deformation of the metal panel leading to imperfections in the outer surface of the vehicle.
There is therefore a need to provide structural reinforcement for the hollow cross-sections of vehicles, which is easily supplied, works well within the bounds of the electrocoat process, provides effective reinforcement to the vehicle both during operation and as crash protection and does not cause deformation of the external body panels of the vehicle during its manufacture.